1. Field of the Invention
The invention relates to a direct current electric arc furnace for melting metal, particularly scrap, which has a furnace vessel that is closable by a cover. The furnace vessel consists of a lower vessel with a refractory-lining and a metallic upper vessel through which coolant flows. The arc furnace further has a device for feeding the electric current. The current feeding device consists of an electrode which extends through the cover into the furnace vessel and a bottom electrode located in the bottom of the lower vessel. Both electrodes are connected to a direct current source via feed lines.
2. Description of the Prior Art
In direct current furnaces, the direct current source is usually located on one side of the furnace. As a result of magnetic fields at the high current strengths utilized, the electric conductors which lead to the electrodes in the furnace vessel exert a deflecting force on the arc located between the electrode extending into the furnace and the bottom electrode or the melting bath. The electromagnetic forces acting from the current paths into the melt result in a deflection of the arc before the cathode in the direction of the anode, essentially away from the side from which the current is supplied.
An electric arc furnace is required to melt scrap with maximum productivity without locally increasing the wear rate of the furnace vessel. In known arc furnaces, the attempt has therefore been made to center the arc.
A direct current electric arc furnace is known from DE 32 05 270 A1 in which both the positive and negative conductors are drawn together to a point in the furnace structure, from which the individual conductors run in a specified manner above the furnace, parallel from there to the furnace axis on a plane below the furnace, and finally to the floor electrode. This arrangement of conductors is not only elaborate in design, but also cost-intensive. Furthermore, it limits the accessibility of the furnace to a unacceptable extent.
A direct current electric furnace for melting metal is known from EP 0 255 793 B1, in which, in order to break down the arc deflection effect, a magnetic screen is arranged on the bottom of the vessel in such a form as to cover the portion of the bottom that encompasses a hearth electrode and at least a portion of the corresponding return line. The metal portion of the lower furnace part known from the aforementioned reference has a metal plate with high magnetic permeability, which must be taken into account as the furnace is being constructed.
So that the electromagnetic fields produced by currents below the vessel bottom exert an adequate influence on the electric arc, the vessel mantle in this area consists of expensive, non-magnetic material, as a rule, high-grade steel.